In a full-face-type helmet or the like, when a regular shield (to be referred to as a “main shield” in this DESCRIPTION) tends to fog as in the rain, a shield structure is sometimes employed in which an anti-fogging auxiliary shield referred to as an anti-fogging sheet or the like is mounted on the main shield, as disclosed in, e.g., WO 01/13750 A1 (to be referred to as “the prior patent reference” hereinafter). In the helmet shield structure (to be referred to as “the shield structure of the prior patent reference” hereinafter) disclosed in the above prior patent reference, the anti-fogging auxiliary shield is detachably mounted on the inner surface of the main shield to maintain a slight gap with respect to the main shield. In this case, substantially semicircular left and right engaging notched recesses are formed in the left and right ends, respectively, of the anti-fogging inner auxiliary shield. Left and right engaging headed shafts respectively having removal preventive heads for the anti-fogging inner auxiliary shield are disposed on the main shield to correspond to the left and right engaging notched recesses (that is, engaging slits), respectively, such that the headed shafts project on the inner surface of the main shield. Such engaging headed shafts have eccentric shaft structures so that they can adjust the tension of the anti-fogging auxiliary shield with respect to the main shield. Also, the non-eccentric shafts of the engaging headed shafts on the proximal end sides are pivotally inserted in mounting holes of the main shield from the outer surface side of the main shield. The removal preventive heads are fixed to the eccentric shafts. Hence, the tension can be adjusted by pivoting the eccentric shafts.
In the shield structure of the prior patent reference as described above, when mounting the anti-fogging inner auxiliary shield on the inner surface of the main shield, the left and right engaging headed shafts of the main shield are sequentially, relatively engaged with the left and right engaging notched recesses, respectively, of the anti-fogging inner auxiliary shield. This engaging may be done by sequentially, relatively introducing the left and right ends of the anti-fogging inner auxiliary shield into the eccentric shafts existing between the removable preventive heads of the left and right engaging headed shafts and the inner surface of the main shield. When removing the anti-fogging inner auxiliary shield from the main shield, the left and right engaging headed shafts may be sequentially, relatively removed from the left and right engaging notched recesses, respectively, by performing operation reverse to that for engaging. With the shield structure of the prior patent reference having the arrangement as described above, a sealed space serving as a heat-insulating layer can be formed between the outer main shield and the inner anti-fogging auxiliary shield. The heat-insulating layer can serve to decrease the temperature difference between the inner and outer sides of each of the two shields, thus anti-fogging both the main shield and anti-fogging inner auxiliary shield.
In the full-face-type helmet or the like, when the rider travels a bad road as in motocross, the main shield tends to become dirty with mud or the like. For this reason, a shield structure may be used in which one or a plurality of layers of mudguard auxiliary shields each called a mudguard sheet, tear-off film, disposable sheet, or the like are mounted on the outer surface of the main shield such that they can be sequentially removed, as disclosed in the homepage of SHOEI CO., LTD. (http://jp.shoei.com/products/ja/parts_list.php?parts_id=1) (to be referred to as “the prior non-patent reference” hereinafter). In the shield structure (to be referred to as “the shield structure of the prior non-patent reference” hereinafter) for the helmet on which the mudguard outer auxiliary shield is mounted in this manner, left and right engaging holes are formed in the left and right ends, respectively, of the mudguard outer auxiliary shield. Each engaging hole is formed of a substantially circular center hole and a pair of upper and lower slits extending from the center hole outward along the diameter in opposite directions. Left and right engaging headed shafts respectively having removal preventive heads for the mudguard outer auxiliary shield are disposed on the main shield to correspond to the left and right engaging holes, respectively, such that the head shafts project on the outer surface of the main shield. Such engaging headed shafts have eccentric shaft structures so that they can adjust the tension of the mudguard outer auxiliary shield with respect to the main shield. Also, set screws inserted in the mounting holes of the main shield are screwed in the non-eccentric shafts of the engaging headed shafts at the proximal end sides from the inner surface side of the main shield. This fixes the engaging headed shafts to the main shield. Hence, the set screws are loosened by pivoting the engaging headed shafts, the engaging headed shafts and set screws are entirely pivoted by an appropriate amount, and after that the engaging headed shafts are pivoted with respect to the set screws so that the set screws are screwed in and fixed to the engaging headed shafts again. Then, the tension can be adjusted.
In the shield structure of the prior non-patent reference, when mounting the mudguard outer auxiliary shield on the outer side of the main shield, the left and right engaging headed shafts of the main shield are sequentially, relatively engaged with the left and right engaging holes, respectively, of the mudguard outer auxiliary shield. This engagement may be performed by sequentially, relatively inserting the left and right engaging headed shafts into the left and right engaging holes, respectively, of the mudguard outer auxiliary shield which includes one or a plurality of layers.
In the shield structure of the prior non-patent reference described above, when removing the mudguard outer auxiliary shield (if it includes a plurality of layers, the outermost mudguard outer auxiliary shield) dirty with mud or the like from the main shield, the following operation may be performed. More specifically, first, the operator such as the helmet wearer may hold the mudguard outer auxiliary shield at a portion near its left or right end with the hand and pull it substantially forward. In this case, the left or right (in other words, either one) engaging headed shaft of the main shield is extracted relatively from the left or right engaging hole of the mudguard outer auxiliary shield. Subsequently, when the operator further pulls the mudguard outer auxiliary shield substantially forward with his hand, the right or left (in other words, the other) engaging headed shaft of the main shield is also extracted relatively from the right or left engaging hole of the mudguard auxiliary shield. As a result, the mudguard auxiliary shield can be removed from the main shield completely.
Assume that not only the anti-fogging inner auxiliary shield can be mounted on the main shield employed in the shield structure of the prior patent reference having the above arrangement, but also a mudguard outer auxiliary shield can be mounted on the same main shield as in the case of the main shield employed in the shield structure of the prior non-patent reference. Then, one type of main shield structure can be commonly employed in two types of helmets such as the helmet disclosed in the prior patent reference and the helmet disclosed in the prior non-patent reference. The main shield structure becomes compatible, which is preferable. In this case, left and right engaging headed shafts as those disposed on the main shield of the shield structure of the prior non-patent reference may be disposed on the main shield of the shield structure of the prior patent reference as second engaging headed shafts for the mudguard outer auxiliary shield. More specifically, the second engaging headed shafts are disposed on the main shield to project on the outer surface of the main shield. In this case, however, the main shield structure becomes complicated, and the number of components increases, leading to a high cost. In addition, to mount the anti-fogging inner auxiliary shield and mudguard outer auxiliary shield, the main shield is provided with a large number of engaging headed shafts. This degrades the appearance of the main shield (and accordingly the shield structure).
Assume that not only the mudguard outer auxiliary shield can be mounted on the main shield employed in the shield structure of the prior non-patent reference, but also an anti-fogging inner auxiliary shield can be mounted on the same main shield as in the case of the main shield employed in the shield structure of the prior patent reference. Then, one type of main shield structure can be commonly employed in two types of helmets such as the helmet disclosed in the prior non-patent reference and the helmet disclosed in the prior patent reference. The main shield structure becomes compatible, which is preferable. In this case, left and right engaging headed shafts as those disposed on the main shield of the shield structure of the prior patent reference may be disposed on the main shield of the shield structure of the prior non-patent reference as second engaging headed shafts for the anti-fogging inner auxiliary shield. More specifically, the second engaging headed shafts are disposed on the main shield to project on the inner surface of the main shield. In this case, however, the main shield structure also becomes complicated, and the number of components increases, leading to a high cost. In addition, to mount the mudguard outer auxiliary shield and anti-fogging inner auxiliary shield, the main shield is provided with a large number of engaging headed shafts. This degrades the appearance of the main shield (and accordingly the shield structure).
Furthermore, in the case of the shield structure of the prior non-patent reference, when adjusting the tension of the mudguard outer auxiliary shield with respect to the main shield, as described above, the set screws must be loosened by pivoting the engaging headed shafts, the engaging headed shafts and set screws must be entirely pivoted by an appropriate amount, and after that the engaging headed shafts must be pivoted with respect to the set screws so that the set screws are screwed in and fixed to the engaging headed shafts again. This leads to cumbersome tension adjusting operation. In particular, when traveling a bad road on a motorbike as in motocross, the mudguard outer auxiliary shield tends to become dirty with mud or the like. Therefore, if a plurality of layers of mudguard outer auxiliary shields are mounted on the outer surface of the main shield, they must be sequentially removed one by one within a comparatively short time interval. Every time an outer auxiliary shield is to be removed (in other words, within a comparatively short time interval), the tension of a new mudguard outer auxiliary shield existing under the removed mudguard outer auxiliary shield must be adjusted. In this case, adjustment of the tension of the mudguard outer auxiliary shield is further complicated.